Fuel injector with pilot injection



Sept. 1963 M. VANDER ZEE ETAL 3,104,317

FUEL INJECTOR WITH PILOT INJECTION Filed Sept. 5, 1962 2 Sheets-Sheet 1 INVENTOR. f/f/c/nei I/anaer Zee ATTORNEY Sept. 24, 1963 M. VANDER ZEE ETAL 3,104,317

FUEL INJECTOR WITH PILOT INJECTION 2 Sheets-Sheet 2 Filed Sept. 5, 1962 INVENTOR. mama; /am/e/'Zee BY 317776! fFLzz/zm ATTORNEY United States Patent 3,194,817 FUEL INJECTOR WITH PILG'I INJECTION Michiel Vanrler Zee, Grand Rapids, and Elmer Bluhm,

Grandville, Mich, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Sept. 5, 1962, Ser. No. 221,563 4 Claims. (1. 239-90) This invention relates to fuel injection devices such as are used for delivering metered amounts of fuel to internal combustion engines, and particularly to such devices wherein the injection is effected in two distinct phases, i.e., a pilot or primary injection and a main or secondary injection with a gap or time interval therebetween.

Injection of the fuel in this manner is advantageous,

particularly with diesel engines, because the primary injection charge which can be made relatively small in quantity serves to initiate the combustion in the engine cylinder in advance of the main charge, thereby reducing the rate of pressure rise and the peak pressure developed in the combustion chamber, with consequent increased efiiciency and lowering of the noise level of the combustion process. While it has herefore been proposed to accomplish this by mechanical means through the addition of an extra groove or control edge on the plunger and additional ports in the bushing of a conventional jerk type injector, substantially less harshness and wear on the operating parts can be obtained with the use of a hydraulically controlled valve in the pump delivery line to the injection nozzle. An arrangement of the latter type is disclosed in US. Patent No. 2,951,643 to Engel, Jr., wherein the charge forming pressure is maintained in the pumping chamber during the interval between the primary and main injections. Although this feature in Engel, Jr. was intended to assure precise timing of the end of the primary injection and start of the main injection, it has been found that under high speed operating conditions, either because of expansion of the parts or the, extreme rapidity of the shuttle valve movement under the high fuel pressures developed, the intended obective was not obtained. It is the object of the present invention to provide an Improved fuel injector with pilot injection which overcomes the disadvantages of the prior art, and wherein a second plunger operates in the pumping chamber to develop the actual injection pressure in response to fuel pressure forces applied to it by the main or mechanically driven plunger. By suitably porting the pumping chamber and providing a passage in the second plunger, the latter acts somewhat in the manner of a shuttle valve to separate the fuel injection into respective primary and secondary phases. During the period of interruption between these phases the injection fuel pressure in the pumping chamber is vented to the pump supply or reservoir chamber, with the result of making such interruption more positive and thereby insure obtaining the advantages in engine combustion referred to above.

The invention will be more clearly understood from the following description, having reference to the drawings, wherein: v

FIGURE 1 is a longitudinal sectional view through a portion of an internal combustion engine, incorporating a unit fuel injector constructed in accordance with the invention;

FIGURE 2 is an enlarged fragmentary sectional view, similar to that of FIGURE 1 but showing the hydraulic control features of the injector pump in greater detail; and

FIGURE 3 is a sectional view taken substantially along the line 3-3 of FIGURE 2.

3 I 94,8 1 7 Patented Sept. 24, 1963 ice Referring now in detail to the drawings and first to FIGURE 1, an internal combustion engine cylinder head is indicated at 1 in which is mounted a unit fuel injector 2. The lower end of this injector terminates in a fuel nozzle spray tip 3 on the combustion chamber side 4 of the cylinder head. Within the stationary body 5 of the injector is shown the usual fixed bushing 6 in which reciprocates a first plunger element 7. Below the bushing 6 is a second bushing 8 in which is slidably fitted a second plunger 9. Intermediate the adjacent ends of the bushings 6 and 8 is a plate-like spacer 10 with a central aperture 11 which is slightly smaller than the bore 12 of the lower bushing 8 and serves to limit upward travel of the second plunger 9. The bore 12, aperture 11 and bore 13 of the upper bushing 6 together consutute the pumping chamber designated generally by the numeral 14. Means for drivingly reciprocating the upper plunger 7 may conventionally comprise a rocker 15 journaled on a shaft 16 supported above the cylinder head and operated by an engine cam 17. A plunger return spring 18 cooperates with the rocker 15 in effecting plunger reciprocation. Inlet fuel supply and return fuel passages (not shown) in the body 5 connect respective external fittings (one of which is shown at 19) with a fuel reservoir chamber 21 which extends annularly'and axially above both the bushings 6 and 8 within the body 5.

As best shown in FIGURE 2, this reservoir chamber 20 is connected to the pumping chamber 14 by a first port 21 which extends through the side of the upper bushing 6 at a point below the plunger 7 when the latter is in its uppermost position, shown. A passage, comprising an axial hole 22 in the lower end of the plunger '7, a connecting transverse hole 23 and a relief groove 24 about the periphery of the plunger 7, operate in conventional manner to connect the pumping chamber 14 with the reservoir chamber 20 Via the port 21 to limit the effective stroke of the plunger 7, in a well known manner.

That is to say, during the downward stroke of the plunger 7, it traverses the port 21, initially closing it to entrap fuel between the two plungers until the passage 222324 moves into communicating registry with the port 21, bypassing such fuel pressure to the reservoir chamber 20. V

One or more radial ports 25 extend through the lower bushing 8 to also connect the reservoir chamber 20' with that portion of the pumping chamber below the lower plunger 9 whenthe latter is in its upper-most position against the stop plate 10, as shown. This second plunger 9, it will be noted, has a passage connecting its lower end with the side of the plunger 9 inter-mediate the ends thereof, which passage comprises an axial portion 26 and a connecting transverse portion 27. This latter passage 26-27 is normally closed against fuel flow erethrough by the side or bore 12 of the lower bushing, but upon sufficient downward travel of the lower plunger 9 the port or ports 25 register with this passage to vent the lower end of the pumping chamber 14 to the reservoir chamber. A spring 28 biases the lower plunger upwardly against the stop plate it but this spring is su-fficiently yieldable to accommodate downward movement of the plunger 9 under fuel pressure forces developed between the plungers by the advancement of the upper plunger 7. The lower end of the pumping chamber 14 terminates in an outlet 29 through which fuel displaced by the plunger 9 is delivered. In the arrangement shown, this outlet is in the form of a central aperture provided in a spacer plate 30 positioned between the lower bushing 8 and the spray tip 3. The latter is hollow and contains a valve 32 biased by a spring 33 to close the outlet 29, up,- stream of the valve 32. The interior of the spray tip terminates in spray orifices 34 through which the injection fuel enters the engine combustion chamber.

During operation, as is believed clear from the foregoing description, with each downward or injection stroke of the driven plunger '7 fuel is entrapped between it and the lower plunger 9' immediately following closing of the upper port 21. The resulting fuel pressure rise in the pumping chamber between the two plungers forces the lower plunger downward against its spring 28, closing the lower ports 25 and cut-rapping fuel in the lower end of the pumping chamber. The resulting pressure rise below the plunger 9 forces the injection valve 32 off its seat, allowing fuel to be displaced from the lower end of the pumping chamber into the spray tip 3 and thence out the orifices 34. After the lower plunger 9 has moved downwardly a sufiicient distance for the ports 25 to register or communicate with the lower plunger passage 26-217 this injection pressure is relieved via the ports 25 to the supply side of the pump as represented by the reservoir chamber 20, and injection ceases. Continued downward movement of the upper plunger 7, however, forces the lower plunger 9 further downward, out of registry between the ports 25 and the passage 26-27, reinstituting fuel injection. Eventually, upon the upper plunger 7 moving downward sufiieient to eifect registry of its passage 222324 with the upper port 21, the fuel pressure between the two plungers is biased or vented to the reservoir chamber and no further downward movement of the lower plunger occurs, thus end-' ing the main" injection. The springs 28 and 33 then return the plunger 9 and injection valve 32 to their initial positions shown, preparatory to the next injection cycle, and the upper plunger return spring 13 likewise retracts plunger 7 as the engine cam permits its return to starting position.

Thus it will be appreciated that the invention serves to provide for obtaining a pilot injection, followed by a brief interval of no injection, before the main injection stage. Also, by reason of the novel arrangement described the injection pressure is relieved during the period of interruption, thereby making such interruption positive so as to insure initiating combustion in the engine cylinder in advance of the main charge. Obviously, the relative durations of the primary and main injections, as well as the length of the period of interruption therebetween, may be selected through proper dimensioning of the ports, plungers, etc., as desired. While only a single preferred embodiment of the invention has been disclosed, it is appreciated that numerous minor changes in the construction and arrangement of the parts may be made without departing from the spirit and scope of the invention as defined in the following claims.

We claim:

1. In a fuel injection device, a fuel charge forming ing chamber between said plungers, said second plunger being movable in response to said fuel pressure between the plungers to traverse the second port and thereby entrap fuel inwardly of the pumping chamber from said second port and displace said entrapped fuel from the pumping chamber, and an outlet for fuel displaced from the pumping chamber by said second plunger, said sec- 0nd plunger having a passage interconnecting one side thereof intermediate its ends and its end inwardly of the pumping chamber, said passage being normally closed at its end intermediate the ends of the second plunger by v the side of the pumping chamber but registerable with said second port to relieve the pressure of said entrapped fuel and thereby interrupt its displacement via said outlet prior to termination of movement of the second plunger inwardly of the pumping chamber.

2. The invention of claim 1 wherein said first plunger has a passage interconnecting one side thereof intermediatev its ends and its end inwardly of the pumping cham.

ber, said last named passage being normally closed at its end intermediate of the ends of the first plunger by the side of the pumping chamber prior to start of movement of the second plunger, but registerable with said first port to relieve said fuel pressure between the plungers and thereby terminate said fuel displacement by the second plunger after the first plunger has completed a pre determined portion of its stroke inwardly of the pumping chamber. a

3. The invention of claim 1, together with a valve operative to block flow of fuel through said outlet, means biasing said valve closed, said valve being movable in the opening direction against the force of said biasing means in response to said movement of the second plung er developing a predetermined fuel pressure in the pump- I ing chamber between said outlet and second plunger.

4; The invention of claim 2, together with means biasing said second ber.

References Cited in the file of this patent UNITED STATES PATENTS 2,951,643 Engel Sept. 6, 1960 plunger outwardly of the pumping cham- 

1. IN A FUEL INJECTION DEVICE, A FUEL CHARGE FORMING PUMP INCLUDING A PUMPING CHAMBER, FIRST AND SECOND PLUNGERS RECIPROCABLE THEREIN AND A RESERVOIR CHAMBER EXTERNALLY OF THE PUMPING CHAMBER, SAID PUMPING CHAMBER HAVING FIRST AND SECOND PORTS CONNECTING IT WITH THE RESERVOIR CHAMBER AND OPERATIVELY SPACED FROM EACH OTHER AXIALLY OF THE PUMPING CHAMBER, MEANS FOR DRIVINGLY RECIPROCATING SAID FIRST PLUNGER, SAID FIRST PORT BEING TRAVERSABLE BY SAID FIRST PLUNGER ON ITS PUMPING STROKE TO ENTRAP AND APPLY INCREASING PRESSURE TO FUEL IN THE PUMPING CHAMBER BETWEEN SAID PLUNGERS, SAID SECOND PLUNGER BEING MOVABLE IN RESPONSE TO SAID FUEL PRESSURE BETWEEN THE PLUNGERS TO TRAVERSE THE SECOND PORT AND THEREBY ENTRAP FUEL INWARDLY OF THE PUMPING CHAMBER FROM SAID SECOND PORT AND DISPLACE SAID ENTRAPPED FUEL FROM THE PUMPING CHAMBER, AND AN OUTLET FOR FUEL DISPLACED FROM THE PUMPING CHAMBER BY SAID SECOND PLUNGER, SAID SECOND PLUNGER HAVING A PASSAGE INTERCONNECTING ONE SIDE THEREOF INTERMEDIATE ITS ENDS AND ITS END INWARDLY OF THE PUMPING CHAMBER, SAID PASSAGE BEING NORMALLY CLOSED AT ITS END INTERMEDIATE THE ENDS OF THE SECOND PLUNGER BY THE SIDE OF THE PUMPING CHAMBER BUT REGISTERABLE WITH SAID SECOND PORT TO RELIEVE THE PRESSURE OF SAID ENTRAPPED FUEL AND THEREBY INTERRUPT ITS DISPLACEMENT VIA SAID OUTLET PRIOR TO TERMINATION OF MOVEMENT OF THE SECOND PLUNGER INWARDLY OF THE PUMPING CHAMBER. 